87 votes
Accepted

Why does Io cast a hard shadow on Jupiter, but the Moon casts a soft shadow on Earth?

It's due to the larger relative apparent size of the Sun. When the source of light is a point source the shadow is harder, and when it is extended it is softer. Jupiter is approximately 5 times more ...
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40 votes

Is it possible that the shadow of The Moon is a single dot during solar eclipse?

What you are calling a focal point is the end of the umbra, the point at which the umbra changes to the antumbra. In a total solar eclipse, that point is below rather than above the surface of the ...
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  • 28.3k
39 votes

Can a planet in our system eclipse the sun as seen from another one?

In our solar system, it is possible for one planet to partially eclipse the sun, but it is not possible for any planet to cause a full solar eclipse as seen from another planet. The sun is too big and ...
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34 votes
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Will just a glimpse (less than a second) of sun during partial solar eclipse damage eyes?

Glancing at a partial solar eclipse is about as dangerous as glancing at the Sun on any other day. If you look at the Sun a few minutes after sunrise or a few minutes before sunset, when the Sun's ...
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  • 10.4k
31 votes

Why does Io cast a hard shadow on Jupiter, but the Moon casts a soft shadow on Earth?

Due to the basic proportionality theorem, the width of the boundary of the shadow is $$ w=\frac{\ell D}L\;, $$ where $\ell$ is the distance from the moon to the planet’s surface, $L$ is the ...
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  • 411
30 votes

Is it possible to see mercury transit "clearly" by the naked eye?

I did see the Venus transit before the Sun in 2004. I used no telescope, but of course I used proper solar eclipse glasses to protect my eyes. The black circle was small but clearly visible. But ...
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  • 415
27 votes
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Is it possible to see mercury transit "clearly" by the naked eye?

I'll use the atmosphere as my big natural lens. So I'll watch the upcoming mercury transit at the sunset time where the sun looks bigger than usual. While the Sun and Moon might seem larger at the ...
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  • 31.8k
26 votes

Why is it okay to watch a sunset but not an eclipse?

During a sunset, the Sun is lower in the sky than during most of the day - much lower. Therefore, light from the Sun travels through about 120 miles of dense atmosphere, compared to the roughly 2 ...
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  • 34.1k
23 votes
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Was the Sun's gravitational lensing observed in other solar eclipses than the one in 1919?

Yes, observations of this kind are within the technical scope of amateur astronomers. Several groups succeeded in replicating the experiment during the 2017 eclipse that crossed the USA. For example ...
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  • 91.4k
23 votes

During an eclipse, how big is the shadow of the moon on the earth?

But how big is this shadow? How many kilometers is its diameter? That's a photo of the umbra and penumbra on the surface of the Earth taken from Space. It's a little distorted because it's not ...
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  • 31.8k
22 votes

Can a planet in our system eclipse the sun as seen from another one?

The short answer is no. The alignment occurs, but the eclipse does not, due to the distances and size differences involved. There are a few things to consider here. You already mentioned a lot of them,...
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  • 321
19 votes
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During an eclipse, how big is the shadow of the moon on the earth?

The umbra has a well defined diameter but the size varies due to the eccentricity of the orbits of the Earth and of the Moon. The Moon may be so far away that it can't fill the solar disk at all (for ...
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18 votes

Apparently two objects in Solar Eclipse image

The people who say it is an internal reflection are right. This is an internal reflection inside the lens of the camera. There is no actual object there. In particular, Venus is not visible this ...
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18 votes
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Apparently two objects in Solar Eclipse image

It's an internal reflection. The dead giveaway is that in the second picture, the reflected image is a point reflection at the center of the image optical axis (assuming the image was not cropped). ...
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  • 715
16 votes

Why can't we see a solar eclipse every month?

The Moon orbits in a plane that is inclined with respect to the plane in which the Earth orbits. The intersection between these two planes is a straight line. For an eclipse to occur, this straight ...
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  • 16.8k
15 votes

Is it possible that the shadow of The Moon is a single dot during solar eclipse?

As the Moon's eccentric orbit around the Earth brings it nearer and farther, current solar eclipses can be total or annular. A few in between are hybrid eclipses: total along the midday part of the ...
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  • 16.6k
13 votes

Will just a glimpse (less than a second) of sun during partial solar eclipse damage eyes?

This webpage gives a lot of background information. Key points: It does seem to be the overall dimness of near-total eclipses that allows the pupil to widen enough to allow damaging levels of UV in. ...
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  • 2,525
12 votes

Why does Io cast a hard shadow on Jupiter, but the Moon casts a soft shadow on Earth?

Another factor is involved in addition to the above answers. Io's umbral shadow is a bit over two million kilometers long, almost six times longer than the ~350 thousand kilometer distance between ...
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  • 28.3k
12 votes

Apparently two objects in Solar Eclipse image

I used the same lens flare effect (internal reflections from the camera's optical surfaces) to image the eclipse from my phone. The shape (as well as the location) was a symmetric reflection about the ...
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  • 31.8k
11 votes
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Dark enough to see stars during total solar eclipse?

One thing to double check is if you can see stars easily at night from the same location. If there are city lights nearby, combined with humidity or dust you can have a bright sky due to terrestrial ...
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11 votes
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Could there be an eclipse tomorrow if the Pleiades is covered by the Moon tonight?

Consider how far the pleiades are above the ecliptic, and how far the moon travels in a day. From this you can work the angle at which the moon must travel relative to the ecliptic, in order to cross ...
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  • 4,065
11 votes

Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth?

Let's clarify what "ring of light" you want to cover. In the original photo, the bright spot is the photosphere ("P" in the annotated copy or the original image). The photosphere ...
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  • 7,160
10 votes

Which is more rare: Lunar eclipse or Solar eclipse?

Solar and lunar eclipses occur about equally often - between two and four times per year. However, when you do not intentionally travel around the world chasing solar eclipses, you are more likely to ...
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  • 757
10 votes

Why aren't there eclipses every month when the moon's orbit is aligned with the ecliptic as a result of lunar precession?

There are few things here I think might be worth to state: The tilt of Earth is of no importance here. As the comment says what is of importance how much the Moon orbit is inclined to the ecliptic. ...
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  • 1,452
9 votes

When will the last total solar eclipse occur?

I will take a stab at it. Assuming the last eclipse happens when the moon is at perigee and the earth is at aphelion. the moon's perigee is increasing by 4 cm per year, the earth's aphelion does ...
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  • 256
9 votes
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Can lunar occultation of Venus occur during solar eclipse?

Yes, but such an event would be very rare. Venusian transits last only about 7 hours, and there are only two in 113 years, So Venus is in transit for about 0.0015% of the time. So as a back-of-the-...
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  • 91.4k
9 votes

Why doesn't the moon always follow the same path? Or why aren't the moon's apoapsis and periapsis fixed?

The Moon's orbit about the Earth is only approximately elliptical. The Moon's orbit precesses both axially and nodally, and the eccentricity of the Moon's orbit varies. That the Moon's orbit ...
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  • 28.3k
9 votes
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How to find the the diameter of the moon during a total solar eclipse?

Draw a picture of Sun, moon, observer, as viewed from the side: SSSSSSSSSSSS \ / \ / \ / \ / MMMM \/ Since the triangles ...
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  • 91.4k
9 votes
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Why aren't there eclipses every month when the moon's orbit is aligned with the ecliptic as a result of lunar precession?

The precession of the moon's orbital plane does not align it with the ecliptic plane. The angle between those two planes is approximately 5.14° (it varies by ~±0.15°, mostly due to perturbation by the ...
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  • 10.4k
8 votes
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Viewing a solar eclipse through a leafy tree

It seems that the station has, in fact, given out extremely dangerous advice - simply because it was poorly phrased. Viewing a solar eclipse is incredibly dangerous - mostly under circumstances where ...
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